The present invention relates to composite thermoplastic films and, more particularly, to new and improved composite films of a thermoplastic film and an ethylene terpolymer film and to a process for their preparation.
It is known in the packaging industry to produce composite packaging film to combine the complementary advantageous properties or characteristics of plastics of different families since no single plastic has all the characteristics demanded by the users of the film. Among the properties which one frequently wishes to combine in such films are, in particular, water impermeability and gas impermeability, chemical resistance, especially towards fatty materials, stability to high temperature and to low temperature, weldability, transparency and mechanical strength. If the adhesion between plastics of different families is poor, it is known to use an intermediate layer consisting of a material capable of adhering to each of them, such as, for example, a terpolymer of ethylene, acrylic or methacrylic acid and sodium acrylate or methacrylate.
The composite films of the prior art, however, have not proven to be entirely satisfactory and the packaging industry is constantly looking for improvements, particularly with respect to the mechanical properties, weldability and adhesion of composite films.